Fluorescence spectroscopy artefacts

Pattern recognition is a powerful tool in the identification of archaeological artefacts. A typical example of a pattern recognition application in chemistry is the classification of obsidian artefacts by Kowalski et. al. C1623. A total of 45 obsidian samples from different sources in northern California and 27 archaeological obsidian artefacts of unknown origin were analyzed by X-ray fluorescence spectroscopy. 

Raman spectroscopy has been widely used to study the composition and molecular structure of polymers [100, 101, 102, 103, 104]. Assessment of conformation, tacticity, orientation, chain bonds and crystallinity bands are quite well established. However, some difficulties have been found when analysing Raman data since the band intensities depend upon several factors, such as laser power and sample and instrument alignment, which are not dependent on the sample chemical properties. Raman spectra may show a non-linear base line to fluorescence (or incandescence in near infrared excited Raman spectra). Fluorescence is a strong light emission, which interferes with or totally swaps the weak Raman signal. It is therefore necessary to remove the effects of these variables. Several methods and mathematical artefacts have been used in order to remove the effects of fluorescence on the spectra [105, 106, 107]. 

A treatment for analysing the excitation and fluorescence multiwavelength polarized decay surfaces has been given for the case of a mixture of noninteracting species. An improved model for analysis of fluorescence anisotropy measurements has been presented. Limitations to the use of intense excitation pulses in fluorescence and thermal lens spectrophotometers are discussed in terms of optical saturation. Such artefacts can be eliminated by reference to the fluorescence quantum yield of Rhodamine 6G. A model has been given to describe spectral diffusion in time-resolved hole-burning spectroscopy. ... 

Enderleln J, Gregor I, Patra D, Fitter J (2004) Art and artefacts of fluorescence correlation spectroscopy. Curr Pharm Biotechnol 5(2) 155-161... 

As in absorption spectroscopy, instrumental polarization effects can yield unwanted artefacts and therefore it is appropriate to introduce depolarizers into the optical path before and after the sample if the aim is to monitor the true unpolarized fluorescence spectrum. Unfortunately, this will reduce the light levels com-mensurately and is therefore frequently not pursued. Other methods, involving the use of polarizers set at magic angles to minimize some unwanted polarisation effects have been devised, but are even less frequently employed. 

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